Light emitting device with nanostructured phosphor

ABSTRACT

Embodiments of the invention include a light emitting device, a first wavelength converting material, and a second wavelength converting material. The first wavelength converting material includes a nanostructured wavelength converting material. The nanostructured wavelength converting material includes particles having at least one dimension that is no more than 100 nm in length. The first wavelength converting material is spaced apart from the light emitting device.

CROSS-REFERENCE TO PRIOR APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/398,764, filed Nov. 4, 2014, which is the U.S. National Phaseapplication under 35 U.S.C. 371 of International Application No.PCT/IB2013/053491, filed May 2, 2013, which claims the benefit of U.S.Patent Application No. 61/646,495, filed on May 14, 2012. U.S. patentapplication Ser. No. 14/398,764, International Application No.PCT/IB2013/053491, and U.S. Patent Application No. 61/646,498 are herebyincorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to a semiconductor light emitting devicesuch as a light emitting diode combined with a nanostructured phosphor.

BACKGROUND

Semiconductor light-emitting devices including light emitting diodes(LEDs), resonant cavity light emitting diodes (RCLEDs), vertical cavitylaser diodes (VCSELs), and edge emitting lasers are among the mostefficient light sources currently available. Materials systems currentlyof interest in the manufacture of high-brightness light emitting devicescapable of operation across the visible spectrum include Group III-Vsemiconductors, particularly binary, ternary, and quaternary alloys ofgallium, aluminum, indium, and nitrogen, also referred to as III-nitridematerials. Typically, III-nitride light emitting devices are fabricatedby epitaxially growing a stack of semiconductor layers of differentcompositions and dopant concentrations on a sapphire, silicon carbide,III-nitride, or other suitable substrate by metal-organic chemical vapordeposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxialtechniques. The stack often includes one or more n-type layers dopedwith, for example, Si, formed over the substrate, one or more lightemitting layers in an active region formed over the n-type layer orlayers, and one or more p-type layers doped with, for example, Mg,formed over the active region. Electrical contacts are formed on the n-and p-type regions.

III-nitride devices may be combined with wavelength converting materialssuch as phosphors, as is known in the art, to form white light or lightof other colors. Wavelength converting materials absorb light emitted bythe light emitting region of the III-nitride device and emit light of adifferent, longer wavelength. Wavelength-converted III-nitride devicesmay be used for many applications such as general illumination,backlights for displays, automotive lighting, and camera or otherflashes.

SUMMARY

It is an object of the invention to provide an efficient wavelengthconverted light emitting device.

Embodiments of the invention include a light emitting device, a firstwavelength converting material, and a second wavelength convertingmaterial. The first wavelength converting material includes ananostructured wavelength converting material. The nanostructuredwavelength converting material includes particles having at least onedimension that is no more than 100 nm in length. The first wavelengthconverting material is spaced apart from the light emitting device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates intensity as a function of wavelength for ared-emitting phosphor and a red-emitting nanostructured phosphor.

FIG. 2 illustrates a structure including an LED, a wavelength convertinglayer, and a nanostructured wavelength converting material that isspaced apart from the LED.

FIGS. 3A and 3B illustrate patterns of wire that may be used in ananostructured wavelength converting material to dissipate heat.

FIG. 4 illustrates a structure including an LED, a wavelength convertinglayer that extends over the sides of the LED, and a nanostructuredwavelength converting material that is spaced apart from the LED.

FIG. 5 illustrates a structure including a wavelength converting layerand a nanostructured wavelength converting layer that are both spacedapart from an LED.

FIG. 6 illustrates a structure including an LED and a single wavelengthconverting region.

FIG. 7 illustrates a structure including a sealed nanostructuredwavelength converting layer.

FIG. 8 illustrates a portion of a nanostructured wavelength convertinglayer and a reflector.

DETAILED DESCRIPTION

As used herein, “pump light” refers to light that is emitted by asemiconductor light emitting device such as an LED. “Converted light”refers to pump light that is absorbed by a wavelength convertingmaterial and reemitted at a different wavelength.

The efficiency of a light source such as an LED combined with one ormore wavelength converting materials may be less than optimal for atleast two reasons.

First, devices that emit white light often include a wavelengthconverting material such as phosphor that emits red light. Somered-emitting phosphors emit at least some light at wavelengths outsidehuman eye-response curve. This light is effectively lost for mostapplications. In addition, the gamut for the human eye-response curveranges from about 380 nm to about 780 nm with a peak maximum at 555 nm.The human eye has different sensitivity at different wavelengths. Forexample, the human eye can detect a flux of just 10 photons/s at awavelength of 555 nm but requires 214 photons/s at 450 nm and 126photons/s at 650 nm. Since the human eye is not very sensitive to red(650 nm) light, it is desirable for the red-emitting wavelengthconverting material to emit light in a very narrow wavelength band. Thisdesirable red-emitting wavelength converting material behavior isillustrated by peak 1 on FIG. 1, which is a plot of emission strength asa function of wavelength for a red-emitting phosphor. Peak 1 is a steep,narrow peak that is entirely within the human eye-response curve,indicated by dashed line 3 in FIG. 1. Many common red-emittingwavelength converting materials exhibit the less efficient behaviorillustrated by peak 2 in FIG. 1. These materials emit light over abroader wavelength range.

Second, wavelength converting materials that introduce too muchscattering can reduce the efficiency of the device.

In embodiments of the invention, a wavelength-converted semiconductordevice such as an LED includes a nanostructured light-emitting materialthat absorbs pump light and emits converted light. Nanostructuredmaterials are nanometer-sized semiconductor particles of various shapessuch as, for example, rods, cones, spheres, tubes, or any other suitableshape, that are nanometer length scale in at least one dimension.Quantum wells are particles that are nanometer length in scale in onedimension; quantum wires are particles that are nanometer length inscale in two dimensions, and quantum dots are particles that arenanometer length in scale in all 3 dimensions. Nanostructured materialsmay have a surface area to volume ratio of at least 6×10⁵ cm⁻¹ in someembodiments and no more than 1.5×10⁷ cm⁻¹ in some embodiments. In someembodiments, at least one dimension of the nanostructured material isshorter than the nanostructured material's electron wavefunction or Bohratomic radius. This modifies a bulk property such as the semiconductorband gap into a mesoscopic or quantum property which now changes withthe length in the relevant dimension of the nanostructured material. Thenanostructured material may be, in some embodiments, a red-emittingnanostructured phosphor or a nanostructured phosphor emitting light of adifferent color. Nanostructured phosphors may be referred to herein as“quantum dots” or “Qdots”. Examples of suitable materials include CdSe,CdS, InP, InAs, CdTe, HgTe, ZnS, ZnSe, CuInS₂, CuInSe₂, Si, Ge, and anysemiconductor material with a band gap close to that of visible light,i.e. with a band gap no more than 2.0 eV in some embodiments. Thenanostructured material may be, in some embodiments, a light-emittingnanostructured material doped with transition metal ions and/or rareearth metal ions can also emit suitable red light in a narrow wavelengthrange. These materials may be referred to herein as “doped dots” or“Ddots”. Examples of suitable materials include any of the above-listedquantum dot materials including dopants, Cu-doped ZnSe, Mn-doped ZnSe,Cu-doped CdS, and Mn-doped CdS.

The nanostructured material particles may have an average diameter of atleast 2 nm in some embodiments, no more than 20 nm in some embodiments,no more than 50 nm in some embodiments, and no more than 100 nm in someembodiments. In some embodiments, the particles of nanostructuredmaterial have a size distribution of at least 5% in some embodiments andover 30% in some embodiments. For example, the diameters of particlesmay vary between +/−5% of the average diameter in some embodiments andbetween +/−30% of the average diameter in some embodiments. In contrast,conventional powder phosphors often have a particle size of 1 μm ormore. A majority of phosphor particles, for example greater than 99% ofphosphor particles, have a diameter larger than 20 nm. In addition, in ananostructured material, the optical properties such as absorption andemission wavelength may vary with the particle size. In a powderphosphor, two particles of the same material with different sizestypically have the same absorption and emission wavelength.

Nanostructured material particles such as quantum dots are typicallyattached to a ligand that facilitates processing (for example, withoutthe ligand, the particles may fuse to each other to form a large mass).The ligand may be any suitable material. Examples of suitable ligandsinclude carboxylic acid and phosphine functionalized alkane basedmolecules such as oleic acid or tri-octyl phosphine.

In some embodiments, the nanostructured material emits light in a narrowwavelength band. For example, a nanostructured material may have afull-width-half-maximum of at least 20 nm in some embodiments and nomore than 60 nm in some embodiments. The peak wavelength emitted by ared-emitting nanostructured phosphor may be tuned by selecting thecomposition and/or size of the particles. The tunability ofnanostructured materials may be due to the quantum confinement of theexcitons inside the particles. Nanostructured materials exhibit littleor no scattering of visible light.

The use of nanostructured materials presents design challenges. First,due to high surface area-to-volume ratio of nanostructured materials,the structural and chemical properties of these materials may change inthe presence of oxygen and moisture. Such changes may undesirably alterthe optical properties of the nanostructured materials.

Second, the optical properties, such as absorption and emissioncharacteristics, may be degraded by increases in temperature. Forexample, the peak wavelength emitted by nanostructured wavelengthconverting materials may undesirably shift with an increase intemperature due to intrinsic properties of the nanostructured wavelengthconverting material. In addition, the peak intensity emitted bynanostructured wavelength converting materials may decrease withtemperature. State-of-the-art high-brightness LEDs generate heat duringtransformation of electrical energy to photon energy. For example, thejunction temperature of current high brightness LEDs may beapproximately 85° C. when driven at 350 mA of current. Such temperaturecan affect the optical performance of nanostructured materials if thenanostructured materials are directly attached to the LED.

In embodiments of the invention, a device including an LED and ananostructured wavelength converting material is packaged to efficientlyremove heat from the nanostructured wavelength converting material andto protect the nanostructured material from oxygen and moisture. Thefollowing figures illustrate embodiments of the invention.

As a preliminary matter, one or more semiconductor devices such as LEDsare provided. Any suitable III-nitride LED may be used and such LEDs arewell known. Though in the examples below the semiconductor lightemitting devices are III-nitride LEDs that emit blue or UV light,semiconductor light emitting devices besides LEDs such as laser diodesand semiconductor light emitting devices made from other materialssystems such as other III-V materials, III-phosphide, III-arsenide,II-VI materials, ZnO, or Si-based materials may be used.

LED 10 in the following figures may be, for example, a flip chip deviceconfigured to emit a majority of light from the top surface of the LED.To form such an LED, a III-nitride semiconductor structure is firstgrown on a growth substrate, as is known in the art. The growthsubstrate may be any suitable substrate such as, for example, sapphire,SiC, Si, GaN, or composite substrates. The semiconductor structureincludes a light emitting or active region sandwiched between n- andp-type regions. An n-type region may be grown first and may includemultiple layers of different compositions and dopant concentrationincluding, for example, preparation layers such as buffer layers ornucleation layers, and/or layers designed to facilitate removal of thegrowth substrate, which may be n-type or not intentionally doped, and n-or even p-type device layers designed for particular optical, material,or electrical properties desirable for the light emitting region toefficiently emit light. A light emitting or active region is grown overthe n-type region. Examples of suitable light emitting regions include asingle thick or thin light emitting layer, or a multiple quantum welllight emitting region including multiple thin or thick light emittinglayers separated by barrier layers. A p-type region may then be grownover the light emitting region. Like the n-type region, the p-typeregion may include multiple layers of different composition, thickness,and dopant concentration, including layers that are not intentionallydoped, or n-type layers. The total thickness of all the semiconductormaterial in the device is less than 10 μm in some embodiments and lessthan 6 μm in some embodiments.

A metal p-contact is formed on the p-type region. If a majority of lightis directed out of the semiconductor structure through a surfaceopposite the p-contact, such as in a flip chip device, the p-contact maybe reflective. A flip chip device may be formed by patterning thesemiconductor structure by standard photolithographic operations andetching the semiconductor structure to remove a portion of the entirethickness of the p-type region and a portion of the entire thickness ofthe light emitting region, to form a mesa which reveals a surface of then-type region on which a metal n-contact is formed. The mesa and p- andn-contacts may be formed in any suitable manner. Forming the mesa and p-and n-contacts is well known to a person of skill in the art.

The semiconductor structure may be connected to a support through the p-and n-contacts. The support is a structure that mechanically supportsthe semiconductor structure. The support is a self-supporting structuresuitable to attach to a structure on which LED 10 is mounted. Forexample, the support may be reflow-solderable. Any suitable support maybe used. Examples of suitable supports include an insulating orsemi-insulating wafer with conductive vias for forming electricalconnections to the semiconductor structure, such as a silicon wafer,thick metal bonding pads formed on the semiconductor structure, forexample by plating, or a ceramic, metal, or any other suitable mount.The growth substrate may be removed, or it may remain part of thedevice. The semiconductor structure exposed by removing the growthsubstrate may be roughened, patterned, or textured to increase lightextraction.

Nanostructured wavelength converting layer 12 in the following figuresincludes a light-emitting material, such as the Qdots or Ddots describedabove, and a matrix material in which the nanostructured light-emittingmaterial is disposed. The nanostructured light-emitting material may berandomly or orderly arranged Qdots or Ddots in the matrix. Thenanostructured wavelength converting material particles can be eitherbonded (covalent or ionic or coordination) to the matrix or mechanicallyor physically trapped in the matrix. In some embodiments, the particlesof nanostructured wavelength converting material are formed intoclose-packed or ordered films, where neighboring particles physicallycontact one another. Ordered films of nanostructured particles can beself-assembled by, for example, suspending the particles in a solventthen allowing the particles to settle into an ordered film as thesolvent dries. Alternatively, ordered films of nanostructured particlescan be formed by floating the nanostructured particles on a liquidsurface that is not miscible with the particles. As the particles float,they can be physically pushed together and then transferred as anordered array on to a substrate, which can then be used in one of thearrangements described below.

In some embodiments, close proximity of one particle to another isundesirable because neighboring particles may quench each other'sfluorescence properties or change the peak emission wavelength. Forexample, the closer the spacing between neighboring particles, the morered-shifted the emission wavelength becomes. The spacing betweenneighboring particles may be at least 5 nm in some embodiments, at least10 nm in some embodiments, at least 20 nm in some embodiments, no morethan 100 nm in some embodiments, no more than 500 nm in someembodiments, and no more than 1 μm in some embodiments.

In some embodiments, the nanostructured material particles are coatedwith a shell that repels other particles of nanostructured material. Insome embodiments, the matrix is selected to provide adequate separationof neighboring particles in a miscible fashion (i.e. separation with noaggregation or clustering of the nanostructured particles). In someembodiments, matrix materials that cause aggregation of nanostructuredparticles during film formation or operation of the device are avoided.In some embodiments, matrix materials that maintain their shape duringoperation of the device, that are optically and chemically stable withrespect to temperature, blue flux, and nanostructured particleionization are used. (Ionization refers to the nanostructured materialsemitting electrons from nanostructured particle surfaces.)

Examples of suitable matrix materials include, for example, air ordielectric materials (polymer or ceramic), organic materials (such aspolyethylene (HDPE, LDPE), polypropylene, polyvinyl halide, polystyrene,polyvinylidene halide, polyalkyl methacrylate, poly tetrafluoroethylene, polychloro fluoro ethylene, polyamide 6, polyamide 66,polyimide, polyamide-imide, polyurethane, polycarbonate, polyacetal,polyethylene terephthalate, cellulose acetate butyrate, cellulosenitrate, acrylonirile-butadiene-styrene polyvinyl formal, silicone,polysulfone, thermanox, thermoplastic elastomer, polymethyl pentene,parylene or crosslinked polymers or inorganic materials (such as sol-gelbased silica, titania, zirconia or combination of these and glassceramics), or composites. Composites include mixtures of materials thatare optimized for particular properties. For example, glass beads may bemixed with a polymer to form a mixture with increased viscosity ascompared to the polymer alone. In another example, silicone may be mixedwith an organic polymer to form a mixture with desired solubility. Insome embodiments, inorganic materials are mixed with organic or siliconematerials to form materials with desired properties such as glasstransition temperature, refractive index, and melting point.

Composites can be combinations of dielectric materials and/or metallicmaterials including particulate materials that are nanometer scale in atleast one, two, or three dimensions. For example, claynanoparticle/polymer, metal nanoparticle/polymer, and carbonnanotube/polymer nanocomposites may be suitable. Suitable nanocompositesare commercially available. For example, nylon nanocomposites,polyolefin nanocomposites, M9 (Mitsubishi), Durethan KU2-2601 (Bayer),Aegis NC (Honeywell), Aegis TM Ox (low oxygen transmissionrate—Honeywell), or Forte nanocomposites (Noble) and combinations of theabove-described materials can be used. Nanoclay nanocomposites such asnanomers (Nanocor), closite (Southern Clay products), Bentone(Elementis), Polymer-pellet (PolyOne, Clariant, RTP), Nanofil(Sud-Chemie), Planomers (TNO), Planocolors (TNO), PlanoCoatings (TNO)can be used alone or in combination with other materials. For example,PlanoCoatings, which may provide excellent transparency and barrierproperties, may be combined with Planomers, which may provide thermalstability. Composites with combinations of polymer/s and nanomaterialsfrom Suncolor Corporation (HTLT1070 or HTLT1070AA) provide excellenttransparency in visible wavelength (380 nm-780 nm) and highglass-transition temperature.

In one example, the nanostructured wavelength converting materialincludes CdSe quantum dots disposed in a shell of CdZnS. The matrix isaliphatic acrylate or silicone. The nanostructured wavelength convertinglayer 12 is 100 μm thick. Nearest neighbor nanostructured particles arespaced at least 5 nm apart and no more than 200 nm apart. Thenanostructured wavelength converting layer 12 may be formed by mixingCdSe/CdZnS core-shell material with the matrix material to form aviscous film that is blade-coated, drop-cast, or otherwise dispensed ona substrate.

In the examples illustrated in FIGS. 2, 4, 5, 6, and 7, a nanostructuredwavelength converting layer is spaced apart from an LED 10. A secondwavelength converting layer, which is often not a nanostructuredwavelength converting layer and may be, for example, a powder or ceramicphosphor layer, may be disposed between LED 10 and the nanostructuredwavelength converting layer 12.

FIG. 2 illustrates an example of a device including a nanostructuredwavelength converting layer. A wavelength converting layer 16 is formedover the top surface of LED 10, in close proximity to LED 10. Wavelengthconverting layer 16 may be one or more conventional phosphors, organicphosphors, organic semiconductors, II-VI or III-V semiconductors, dyes,polymers, or other materials that luminesce. Any suitable phosphor maybe used, including but not limited to garnet-based phosphors,Y₃Al₅O₁₂:Ce, Lu₃Al₅O₁₂:Ce, Y₃Al_(5−x)Ga_(x)O₁₂:Ce,(Ba_(1−x)Sr_(x))SiO₃:Eu (BOSE), nitride-based phosphors,(Ca,Sr)AlSiN₃:Eu, and (Ca,Sr,Ba)₂Si₅N₈:Eu. Wavelength converting layer16 may include a single wavelength converting material or multiplewavelength converting materials which may be mixed together or disposedon the top of LED 10 in separate layers. Wavelength converting layer 16may be, for example, a powder phosphor layer formed by electrophoreticdeposition, dyes or powder phosphors mixed with transparent bindermaterial such as silicone or epoxy that are molded, screen printed,spray coated, or injected over LED 10, or prefabricated wavelengthconverting layers such as ceramic phosphors or phosphors or dyesembedded in glass, silicone, or other transparent materials. Thethickness of wavelength converting layer 16 depends on the materialsused and the deposition technique. Wavelength converting layer 16 may beat least 20 μm thick in some embodiments and no more than 500 μm thickin some embodiments.

LED 10 and wavelength converting layer 16 are positioned in the bottomof a reflective container 20. Reflective container 20 can berectangular, round, conical, or any other suitable shape. Reflectivecontainer 20 may be formed, for example, of polymer, metals, ceramics,dielectric materials, combinations of materials, or any other suitablematerial. In some embodiments, reflective container 20 is formed from orincludes at least one thermally conductive material to conduct heat awayfrom the structures within reflective container 20. In some embodiments,reflective container 20 is configured as or thermally connected to aheat sink. Though FIG. 2 illustrates one LED 10 disposed in reflectivecontainer 20, in some embodiments multiple LEDs 10 are disposed in asingle reflective container.

A nanostructured wavelength converting layer 12 is spaced apart from LED10 and wavelength converting layer 16, for example across a top openingin reflective container 20. A spacing h between the top of wavelengthconverting layer 16 (or the top of LED 10) and the bottom ofnanostructured wavelength converting layer 12 may be at least 1 mm insome embodiments, at least 2 mm in some embodiments, no more than 5 mmin some embodiments, and no more than 10 mm in some embodiments.Nanostructured wavelength converting layer 12 includes, as describedabove, a nanostructured wavelength converting material 13 disposed in amatrix 14. The total thickness of nanostructured layer 12 may be atleast 10 μm in some embodiments, at least 20 μm in some embodiments, nomore than 200 μm in some embodiments, and no more than 2 mm in someembodiments.

Nanostructured wavelength converting layer 12 may be formed by, forexample, one or more of the following processing techniques:dip-coating, spin-coating, drop-casting, inkjet printing,screen-printing, spray-coating, brushing, lamination,electro-deposition, vapor-deposition, extrusion, spinning, calendaring,thermoforming, casting and molding. For example, a nanostructuredwavelength converting material may be mixed with a matrix such as aliquid organic polymer or silicone. The mixture may be disposed overdielectric material 18 using one of the methods listed above.Alternatively, the mixture may be disposed on a substrate such as atransparent plate or film that is then disposed over dielectric material18. The film can be processed and/or cured using heat and/or UV and/orpressure in ambient or inert environment or a special environment asneeded, to transform the liquid matrix material to a solid material inwhich the nanostructured particles are suspended. The film may be shapedor excess material may be removed by one or more processes such ascutting, trimming, polishing, mechanical fastening bonding, sealingwelding, electroplating vacuum metalizing, printing, stamping orengraving. In some embodiments, nanostructured wavelength convertinglayer 12 is formed on a thin, transparent substrate that is thenattached to dielectric material 18 before or after formingnanostructured wavelength converting layer 12 on the substrate.

In some embodiments, in order to enhance dissipation of heat from thenanostructured wavelength converting layer, metallic or ceramic wiresthat conduct heat are formed on or in the nanostructured wavelengthconverting layer 12. The wires may be, for example, at least 1 μm widein some embodiments, no more than 100 μm wide in some embodiments, nomore than 1 mm wide in some embodiments, at least 1 μm thick in someembodiments, at least 10 μm thick in some embodiments, and no more than100 μm thick in some embodiments. The wires may be spaced at least 1 mmapart in some embodiments, no more than 10 mm apart in some embodiments,and no more than 20 mm apart in some embodiments. The wires may be >90%reflective in some embodiments. The wires may be formed in the matrixlayer 14 and may be, for example, random, parallel, or otherwisedisposed in any suitable arrangement. Two examples of patterns for wires22 are illustrated in FIGS. 3A and 3B. In some embodiments, wires 22conduct heat to reflective container 20, which may act as a heat sink ormay be thermally connected to a heat sink. The wires may be formed by,for example, screen printing, sputtering then lithographicallypatterning suitable material, or evaporating a suitable material througha shadow mask. Any suitable conductive material may be used for wires22, including, for example, aluminum, copper, silver, and silver-coatedcopper.

In some embodiments, the space between nanostructured wavelengthconverting layer 12 and wavelength converting layer 16 is totally orpartially filled with a dielectric material 18. Dielectric material 18may be, for example, ambient gas, air, ceramic, alumina, polymer, or oneor a combination of the above-described materials for the matrix ofnanostructured wavelength converting layer 12. The materials ofdielectric material 18 may be selected to conduct heat, orheat-conductive materials may be disposed within dielectric material 18.In some embodiments, one or more wires 22, described above in the textaccompanying FIGS. 3A and 3B, may be embedded in dielectric material 18,instead of or in addition to wires disposed on or in nanostructuredwavelength converting material 12.

In the device illustrated in FIG. 4, wavelength converting layer 16extends over the sides of LED 10.

FIG. 5 illustrates another example of a device including ananostructured wavelength converting layer. The details of LED 10,nanostructured wavelength converting layer 12, wavelength convertinglayer 16, dielectric material 18, and reflective container 20 may be thesame as described above. Both nanostructured wavelength converting layer12 and wavelength converting layer 16 are spaced apart from LED 10.Wavelength converting layer 16 is disposed between LED 10 andnanostructured wavelength converting layer 12. Wavelength convertinglayer 16 is spaced from LED 10 a distance h2, which may be greater than0 mm in some embodiments, at least 1 mm in some embodiments, no morethan 10 mm in some embodiments, and no more than 20 mm in someembodiments. The space between wavelength converting layer 16 and LED 10may be filled with a dielectric 18. Nanostructured wavelength convertinglayer 12 is spaced from wavelength converting layer 16 a distance h1,which may be greater than 0 mm in some embodiments, at least 1 mm insome embodiments, no more than 5 mm in some embodiments, and no morethan 10 mm in some embodiments. The space between nanostructuredwavelength converting layer 12 and wavelength converting layer 16 may befilled with dielectric 24, which may be any suitable dielectric materialdescribed above. Dielectric materials 18 and 24 may be differentmaterials in some embodiments and the same material in some embodiments.The positions of nanostructured wavelength converting layer 12 andwavelength converting layer 16 may be switched in some embodiments suchthat nanostructured wavelength converting layer 12 is disposed betweenLED 10 and wavelength converting layer 16.

FIG. 6 illustrates another example of a device including ananostructured wavelength converting material. The details of LED 10,dielectric material 18, and reflective container 20 may be the same asdescribed above. The device illustrated in FIG. 6 has a singlewavelength converting region 26. This region includes both ananostructured wavelength converting material and a conventionalwavelength converting material. In some embodiments, wavelengthconverting region 26 includes a nanostructured wavelength convertinglayer 12 and a wavelength converting layer 16, described above, formedlayered on one another in contact with each other, with either layer onthe top of the wavelength converting region 26. In some embodiments,wavelength converting region 26 includes a nanostructured wavelengthconverting material and an additional wavelength converting materialmixed together. Such a mixed wavelength converting layer may be formedby any of the techniques described above, with any of the matrixmaterial described above. Wavelength converting region 26 may be atleast 20 μm thick in some embodiments, at least 50 μm thick in someembodiments, no more than 100 μm thick in some embodiments, and no morethan 20 mm thick in some embodiments. Wavelength converting region 26 isspaced from LED 10 a distance h3, which may be greater than 0 mm in someembodiments, at least 1 mm in some embodiments, no more than 10 mm insome embodiments, and no more than 20 mm in some embodiments.

As described above, oxygen and moisture can adversely affect theperformance of nanostructured wavelength converting materials. Thenanostructured wavelength converting materials in the devices describedabove can be protected, for example, by selection of appropriate matrixmaterials, by forming a protective layer over the nanostructuredwavelength converting layer, or by sealing the nanostructured wavelengthconverting layer.

In some embodiments, nanostructured wavelength converting materials 13are embedded in matrix materials 14 with low oxygen and moisturepermeability. For example, suitable low oxygen- and moisture-permeablematerials include inorganic materials such as, for example, glass,ceramics, sol-gel-based titania, silica, alumina, zirconia, and zincoxide. In addition, several polymers exhibit suitably low oxygen andmoisture permeability. The following table 1 lists suitable materialsand their oxygen and moisture permeability. Composites of suitablepolymers and nanostructured wavelength converting materials may inhibitor reduce the moisture and oxygen penetration through the nanostructuredwavelength converting layer. In some embodiments, the water vaportransmission rate is no more than 10⁻⁶ g/m²/day and the oxygentransmission rate is no more than 10⁻³ cm³/m²/day/atm.

TABLE 1 List of some materials and their oxygen and moisturetransmission rates. Water vapor Oxygen transmission rate transmissionrate Material (g/m²/day) (cm³ · mm/m²/day/atm) Polyethylene 1.2-5.970-550 Polypropylene (PP) 1.5-5.9 93-300 Polystyrene (PS) 7.9-4  200-540  Polyethylene 3.9-17  1.8-7.7  terephthalate (PET)Poly(ethersulfone) (PES) 14     0.04 PEN 7.3  3.0 Polyimide 0.4-21 0.04-17   15 nm Al/PET 0.18 0.2-2.99 SiO_(x)/PET 0.007-0.03  ORMOCER(hybrid  0.07 coating)/PET Parylene N 0.59 15.4  Parylene C 0.08 2.8Parylene HT 0.22 23.5  Epoxy 0.94 4   Polyurethane 78.7  Silicone19685    

Source: IEEE Journal of Selected Topics in Quantum Electronics, Vol. 10,No. 1, January 2004, p. 45.

In some embodiments, inorganic or organic materials are deposited on ananostructured wavelength converting layer to reduce the oxygen andmoisture penetration. For example, a coating of Al/alumina or SiO_(x) oran organic-inorganic hybrid coating on polyethylene terephthalate (PET)may reduce both oxygen and moisture penetration through thenanostructured wavelength converting layer. Some suitable polymers suchas parylene-based compounds can be vapor deposited and cross-linked atroom temperature. In another example, alumina, silica, siliconnitride/oxynitride is deposited on the nanostructured wavelengthconverting layer to reduce the oxygen and moisture transmission ratethrough the nanostructured wavelength converting layer. Such coatingsmay be deposited by any suitable method including, for example, plasmaenhanced chemical vapor deposition.

In some embodiments, a seal is formed around the nanostructuredwavelength converting layer 12, as illustrated in FIG. 7. A dielectriclayer 32 forms an enclosure around the bottom and sides ofnanostructured wavelength converting layer 12. A dielectric layer 34 isdisposed over the top of nanostructured wavelength converting layer 12and seals the enclosure formed by dielectric layer 32. Dielectric layer32 may be, for example, alumina, ceramic, or any other suitablematerial. Dielectric layer 34 may be, for example, alumina, glass or anyother suitable material. The thickness h6 of dielectric layer 34 may beno more than 10 mm in some embodiments. The structure illustrated inFIG. 7 includes a wavelength converting layer 16, as described above,disposed over LED 10. A dielectric 30 may be disposed around LED 10 andwavelength converting layer 16. Dielectric 30 may be, for example, air,ceramic, polymer, or any other suitable material. The thickness h7 ofdielectric 30 over wavelength converting layer 16 may be no more than 10mm in some embodiments.

In some embodiments, a reflective layer 28 is disposed overnanostructured wavelength converting layer 12, as illustrated in FIG. 8.The thickness of a wavelength converting layer determines how much pumplight is absorbed by the wavelength converting material. Scatteringcaused by some wavelength converting materials such as powder phosphorseffectively increases the optical thickness of the wavelength convertinglayer. Nanostructured wavelength converting materials cause almost noscattering. As a result, a nanostructured wavelength converting materialmust be thicker than a wavelength converting layer including ascattering material. Thick layers are undesirable because they mustdissipate more heat than thinner layers. Reflector 28 in FIG. 8 isconfigured to be more reflective of pump light, and less reflective ofconverted light. Pump light is therefore reflected back intonanostructured wavelength converting layer 12, where it may beconverted, while converted light passes through reflector 28. Reflector28 effectively doubles the optical thickness of nanostructuredwavelength converting layer 12, allowing a thinner layer to be formedfor a given amount of wavelength conversion. In some embodiments,reflector 28 is a dichroic stack.

Having described the invention in detail, those skilled in the art willappreciate that, given the present disclosure, modifications may be madeto the invention without departing from the spirit of the inventiveconcept described herein. For example, though in the examples describedabove the light emitting device is a semiconductor device, in someembodiments other light emitting devices are used such as organic LEDs,high pressure UV arc lamps, or any other suitable light source.Therefore, it is not intended that the scope of the invention be limitedto the specific embodiments illustrated and described.

The invention claimed is:
 1. A structure comprising: a semiconductorlight emitting device; and a wavelength converting region comprising: ananostructured wavelength converting material configured to absorb pumplight and emit converted light, the nanostructured wavelength convertingmaterial comprising particles having at least one dimension that is nomore than 100 nm in length; a phosphor in direct contact with thenanostructured wavelength converting material; a reflector configured tobe more reflective of pump light and less reflective of converted light;and a transparent matrix in which the nanostructured wavelengthconverting material is disposed; wherein a spacing between thewavelength converting region and the semiconductor light emitting deviceis greater than 0 mm and no more than 10 mm.
 2. The structure of claim 1further comprising a dielectric material disposed between the wavelengthconverting region and the semiconductor light emitting device.
 3. Thestructure of claim 1 wherein the nanostructured wavelength convertingmaterial is disposed in the transparent matrix material in a firstlayer, the phosphor is disposed in a second layer, and the first layeris in direct contact with the second layer.
 4. The structure of claim 3wherein the first layer is layered on the second layer.
 5. The structureof claim 1 wherein the transparent matrix is one of organic polymer andsilicone.
 6. The structure of claim 1 wherein the semiconductor lightemitting device is disposed in a reflective container.
 7. The structureof claim 1 wherein the nanostructured wavelength converting material isconfigured to emit red light.
 8. The structure of claim 1 wherein thephosphor is garnet-based.
 9. The structure of claim 1 further comprisingat least one wire in direct contact with the wavelength convertingregion.
 10. The structure of claim 9 wherein the at least one wire isthermally connected to a heat sink.
 11. The structure of claim 1 furthercomprising a coating disposed on the wavelength converting region toreduce one of oxygen penetration and moisture penetration.
 12. Thestructure of claim 11 wherein the coating is selected from the groupconsisting of alumina, silica, silicon nitride, and silicone oxynitride.13. The structure of claim 11 wherein the coating is a parylene-basedcompound.
 14. The structure of claim 1, wherein the phosphor is mixedwith the wavelength converting material in the transparent matrix.
 15. Amethod comprising: positioning a nanostructured wavelength convertingmaterial, configured to absorb pump light and emit converted light, in apath of light emitted by a semiconductor light emitting device andspaced apart from the semiconductor light emitting device by greaterthan 0 mm and no more than 10 mm, the nanostructured wavelengthconverting material comprising particles having at least one dimensionthat is no more than 100 nm in length; depositing a polymer over thenanostructured wavelength converting material; cross-linking the polymerat room temperature; and disposing a phosphor in direct contact with thenanostructured wavelength converting material.
 16. The method of claim15 wherein the polymer is a parylene-based compound.
 17. The method ofclaim 15 wherein depositing comprises vapor depositing.
 18. The methodof claim 15, comprising mixing the nanostructured wavelength materialwith the phosphor.